a) Field of the Invention
The invention relates to a single-phase induction motor with a starting device.
b) Description of the Prior Art
Motors of this type are used today in numerous areas, for example for driving heating pumps and submerged pumps, for driving compressors and other units. They are operated using alternating current and are essentially intended for low capacities. In the simplest form, single-phase induction motors are neither self-starting nor dependent on direction of rotation. However, in practice both are generally required, which is why a starting device is provided. This determines not only the direction of rotation, but also produces a starting moment. In the simplest form, this starting device comprises an auxiliary coil provided in the support, to which a capacitor is connected in series. This starting device is connected in parallel to the support coil.
In a refined embodiment, at least one part of the actual starting device can be switched off after reaching a predetermined rotational speed in most cases by means of a centrifugal switch. When switching off, as a rule the capacitor capacitance existing at the auxiliary coil is reduced. This technology is known, reference is made to it, for example in SIHI-HALBERG, Grundlagen fur die Planung von Kreiselpumpenanlagen (Fundamental principles for planning centrifugal pump installations), 1978, pages 186 and 187.
Known starting devices operate independently of whether or not they are switched off completely or partially when reaching the nominal rotational speed, so that an approximately uniform starting torque rotating with the rotor is produced when starting the motor. The characteristics of the relative magnetic flux of stator and rotor are represented as ellipses arranged essentially symmetrically about the zero point. In terms of construction, starting devices of this type can be realised according to the state of the art by connecting capacitors next to the auxiliary coil which is required anyway. Capacitors are comparatively expensive components and occupy an increasing amount of space with increasing capacitance.
Starting from this, the object of the invention is to provide an alternative starting device which can be constructed more favourably using other electronic components.